The invention relates to a marine transmission gear unit with double drive where two driving engines are arranged on one side of and parallel to the propeller shaft axis, and on both sides of a gearing assembly having a pinion and a greater wheel, the two driving engines driving the greater wheel by way of the common pinion. The propeller shaft is driven either by both driving engines simultaneously, or by one driving engine at a time via the gearing assembly.
Wellknown marine transmission gear units of the aforementioned type employ spur gears having a multistage design for the reduction of the number of revolutions. The number of reduction stages is dependent upon the type of driving engine used. High speed or gas turbines require a greater reduction ratio and hence more stages than the slower-rotating diesel engines.
Two-fold capacity branchings are provided in order to reduce the large space requirement by such gearing assemblies so that the branching wheels or gears are connected with the pinion gears of the neighboring stage by way of torsion bars. This expedient results in a considerable cost increase.
Moreover, where all gear wheels co-rotate independent of the stage of travel and regardless of which engine drives the gear assembly, the noise level is too great in addition to reduction in the effectiveness and efficiency of the gear assembly. Accordingly, it has not been possible to reduce the number of noise sources and loss sources for certain travel stages such as for the so-called "marching" or "creeping travel" stage.
It would be advantageous to provide smaller and lighter weight gearing assemblies; to reduce the spatial area required for accommodating the gear assembly; to simplify production, inspection and servicing of the gear assemblies; to provide for improved operation of the gear assemblies; to eliminate the need to provide torsion bars for load balancing purposes and to improve the operating efficiency and capacity of the transmission structures.
It would be desirable if the same driving engine could be used on portside and starboard side locations with a reversal of direction easily provided without substantial structural expenditure.